Stem tubes
.065 and bore it out to a perfect fit for the steerer.
1.375" .058 for 31.8 bars
1.125" .058 for 25.4 bars
1.125" .049 for 26.0 bars
stems 90 - 100 mm for under 150lb riders . I use 1.125" .035
stems 105 - 120mm all weights 1.125" .049
all 1" ext stems get .049
all lugged stems get .035 ext. I turn the material for the lugs to .035 thick from either .065 (that has been bored) or .058.

frame tubes
1 1/4 x .058

Mixte tubes
1/2 x .035

People I know seem to be happier with the tubing from Aircraft Spruce. Dillsburg is cheaper for a reason, unfortunately. The stuff I got from Dillsburg is ok, but I know people that have gotten tubes with horrible surface finish from them. You don't notice until you clean off the tube either, because it's covered in grime.

I'm just building my first racks now, so I don't know. I'm estimating 10, but take that with a grain of salt. If you really don't want to buy extra, you can draw it out. The corners don't really take up much more than just going straight.

I bought it on sale. I don't use the pictured dies, I substituted 2 machinery type pulleys. I filled them in with epoxy using a Popsicle stick. Perfect 3/8" radius. Later I turned rollers for it out of steel.